The automatic manufacture of glass articles is carried out by means of glass forming machines such as the ones mentioned above and through forming processes known as the blow-blow, press-blow, or press types.
For the manufacture of articles it is necessary to feed molten glass gobs towards the machine. These molten glass gobs are obtained from a feeder which forms part of an glass melting furnace.
The feeder generally includes a feeder bowl defining an outlet spout; a plate having feeding orifices is placed adjacent to said spout, through which flows a discharge of molten glass; a rotating tube at the bowl aligned with the outlet spout and mounted on a mechanism that controls its rotation and height with respect to said outlet spout so that the glass can be not only homogenized at the feeder bowl but also to regulate the passage of the glass that falls towards the orifice plate; a reciprocating plunger inside the tube and aligned with the outlet spout. This plunger is mounted on a reciprocating mechanism which imparts and controls its speed and reciprocating stroke to push a predetermined quantity of glass towards the orifice plate; and a pair of reciprocating shear blades placed opposite to each other underneath the orifice and mounted on its respective reciprocating mechanism. These blades are used to cut the glass gobs from the current of glass flowing from the orifice.
Usually it is the tube that controls the amount of glass that should come out from the orifice to be cut by the blades. The latter is done in order to provide the weight of the glass gobs that is required to manufacture an article of predetermined weight.
However, it is not always possible to have the real weight of the article agree with the predetermined weight of same. This is due to lack of adjustment of the height of the tube which affects the weight of the gobs and of the articles, and to wear of the orifice, and variations in the level of glass, among others.
In order to achieve control over the weight of the gobs and the finished articles, the U.S. Pat. No. 2,306,789 describes an automatic electromechanical regulator that controls the weight of the gobs. This regulator includes a scale to weight the finished articles and provides a representative signal of the weight and elements that respond to same to operate an electric motor connected with the tube's mechanism in order to regulate the height of the tube with respect to the orifice.
After the mentioned patent, a series of other mechanisms made their appearance to control the height of the tube, such as those described in the U.S. Pat. Nos. 2,479,120 of M. K. Koleda; 3,239,326 of R. E. Tyner; and 3,874,866 of Iacovazzi et al, as well as diverse forms for weighing the finished articles of the glass gobs, such as those described by U.S. Pat. Nos. 3,846,107 of T. V. Foster et al; 4,339,028 of T. Meacle; and 4,165,975 of Kwiatkowski et al.
Trying to obtain a more precise control over the weight of the gobs and the articles, other control systems made their appearance. These systems detect the volume of the gob by means of photo-detecting cameras located at a 90 degrees angle, such as the one which is describe by U.S. Pat. No. 4,205,973 of W. H. Ryan.
However, even though you obtain better control over the height of the tube through measurement of its weight or volume, the problem of lack of adjustment in the weight of the gob persists. This is so because up to now the dynamic process of the system in the generation of movement of the tube was unknown nor had it been taken into consideration. The stated dynamic system in the generation of the tube's movement causes a strong tendency to destabilize the system's control.
The above had an inventor, I. Ayala, establish in his Mexican Patent Appln. Ser. No. 206,561 granted to the same sponsor as the sponsor of the present application, that the conditions that upset the desired weight of the glass gob are the following:
1. The temperature, homogeneity and viscocity of the molten glass;
2. The level of the glass in the feeder bowl which exerts a load on the orifice zone;
3. The wear of the orifice through which the glass flows comes out; and
4. The disarrangements in the tube mechanism.
In spite of the fact that said patent application request already took into account the dynamic of the system, the stated system had only been partially understood. For example, just as was discovered by the inventors of the present patent application, the speed of rotation of the tube not only has a relation with the homogenization of the glass inside the feeder bowl but it also provokes a phenomenon known as "Coriolis effect" which causes suctin through the formation of a spiral or vortex current making it necessary to take into account the stated tube rotation speed in addition to its height. Likewise, the viscosity and the temperature of the glass at the feeder bowl, in combination with the speed and stroke of the plunger within the tube and the speed of the shear blades, are the factors that intervene in the system's dynamics. In addition he also determined that the shape of the glass gobs also influence the system's dynamics which again was reflected in the appropriate shapping of the finished articles. It was found that the form of the gobs could be controlled, taking into account the additional factors previously mentioned, and through the control of rotation and height of the tube, the speed and stroke of the plunger, and the cutting speed of the blades.
Taking into account all of the formerly mentioned parameters, the inventors of the present patent application invented an electronic system that automatically controls both the weight and the shape of the glass gobs. This is done through a continous monitoring of the weight of the finished articles, the rotation speed and height of the tube with respect to the orifice, the speed and stroke of the reciprocating plunger, the temperature, the viscosity and level of the molten glass in the feeder bowl, the cutting speed of the blades that cut the gob, and the shape of the glass gobs. The stated monitoring of all of these factors is carried out through a data processor which compares the real weight of the finished articles with the predetermined weight of same and relates the weight deviations to the rotation speed and height of the tube, to the speed and stroke of the plunger, to the temperature, viscosity and level of the glass in the feeder bowl and to the cutting speed of the blades that cut the gob and to the shape of the gobs. It provides compensation signals on the speed and tube height to its respective mechanism to permit the passage of adequate glass weight between the stated tube and the orifice so as to achieve the predetermined weight and shape of the articles.